The present invention pertains to the synthesis of a carbamate, especially relates to a new method for preparing a carbamate, a catalyst applied in the method, a method for preparing the catalyst and use thereof.
Carbamate is a kind of chemical intermediate that is widely used for preparing various chemical products. For example, methyl carbamates are not only suitable for the preparation of melamine derivatives and polyethylenamine, but they can also be reacted with unsaturated hydrocarbons, aldehydes, ketones, polyols or aromatics to obtain various derivatives. In addition, ethyl carbamate can be used to prepare a kind of promising ataractic, alkanediol dicarbamates (Sidney Beinfest etc, preparation of organic mono-carbamates, U.S. Pat. No. 2,837,561). Furthermore, butyl carbamate can be reacted with formaldehyde to obtain hydroxymethyl derivatives, which can be used as an anti-creasing reagent for textile materials (Max Robeson etc. production of alkyl carbamate, U.S. Pat. No. 3,574,711). Moreover, carbamates are also suitable for preparing the corresponding organic carbonates, or as new carbonylation reagents to prepare isocyanates.
Due to the wide use of carbamates, the method for preparing the same has attracted much attention. U.S. Pat. No. 4,242,520 discloses a method for preparing carbamates by reacting an amine, carbon monoxide (i.e. CO) and a hydroxyl compound in the presence of a catalyst. However, carbon monoxide may potentially harm the health of producers or users, because it is a toxic gas.
Moreover, it was reported that carbon dioxide (CO2) can be used as a carbonylation reagent to replace toxic carbon monoxide in the preparation of organic carbonates (Yoshida, Y., et al., Bull. Chem. Soc. Japan 1989, 62, 1534), in which, CO2 was directly or indirectly applied. For example, U.S. Pat. No. 6,399,808 discloses a method to form organic carbamates by reacting an amine and CO2 in the presence of an organic electrophilic reagent. This method, however, required an anhydrous solvent, and halogenide salts were simultaneously formed with the organic carbamates.
In addition, the urea alcoholysis method was also a mature method widely applied to prepare carbamates. In this method, carbamates are obtained by reacting urea and a hydroxyl group containing compound under proper conditions, wherein CO was avoided during the production. The method can be used under the condition of using a catalyst. Suitable catalysts include zinc oxide as disclosed in U.S. Pat. No. 3,574,711; copper acetate as disclosed in U.S. Pat. Nos. 2,837,561 and 3,013,064; composites of transition metal oxides and acids as disclosed in U.S. Pat. No. 3,554,730; nano-TiO2 and R3N catalyst systems as disclosed in CN 1365969; and metal oxides such as ZnO, MgO, CaO, Pb2O3 etc. as disclosed in CN 1475481. However, the various catalysts disclosed above were not perfect when used in urea alcoholysis methods. One problem is that the carbamate yields were not high. Also, the catalyst was difficult to separate from the reaction products such that it could be recycled.
It is therefore necessary, from an industrial point of view, to develop a new method for preparing carbamates and a new catalyst for the method. It would be desirable for the method to prepare carbamates by reacting substituted urea and hydroxyl groups containing compounds, while allowing for the catalyst to be easily separated and recycled.